A roblox linear velocity script is essentially the secret sauce for anyone trying to move parts with precision instead of just letting the physics engine do whatever it wants. If you've spent any time in Studio lately, you probably know that the old BodyMovers—like BodyVelocity—are officially "legacy" objects. While they still work, the new constraint-based system is much more stable and predictable. LinearVelocity is the modern way to push things around in a straight line, and honestly, once you get the hang of it, you'll never want to go back to the old ways.
Why We Switched from BodyVelocity
Let's be real for a second: BodyVelocity was a bit of a headache. It worked, sure, but it felt clunky and often had weird interactions with other forces. Roblox introduced the LinearVelocity constraint to give us more control. It's part of the new physics API that uses Attachments, which might sound like extra work at first, but it's actually a lifesaver for organization.
When you use a roblox linear velocity script, you're working with a system that calculates force based on the mass of the object and the target speed you want to hit. It feels "snappier." Whether you're making a racing game, a knockback system for a sword, or a simple moving platform, this tool is your best friend.
The Basic Setup: It's All About Attachments
Before we even touch a line of code, you need to understand that LinearVelocity won't do anything unless it has an Attachment to cling to. It's like trying to pull a wagon without a handle—you need that point of connection.
- Insert a Part into your Workspace.
- Inside that Part, add an Attachment.
- Inside the same Part, add a LinearVelocity object.
- In the properties of the LinearVelocity, set the
Attachment0property to the Attachment you just created.
If you skip this step, your script is going to throw errors, or worse, just do absolutely nothing while you scratch your head wondering what went wrong.
Writing Your First Roblox Linear Velocity Script
Now for the fun part. Let's write a simple script that makes a part move forward at a constant speed. This is a great starting point because you can easily modify it for different directions or speeds later.
```lua local part = script.Parent local attachment = part:WaitForChild("Attachment") local linearVelocity = part:WaitForChild("LinearVelocity")
-- Set the velocity direction and speed -- This will move the part 10 studs per second on the X-axis linearVelocity.VectorVelocity = Vector3.new(10, 0, 0)
-- MaxForce is crucial. If it's too low, the part won't move. linearVelocity.MaxForce = 10000
-- Make sure the force is applied relative to the world or the attachment linearVelocity.RelativeTo = Enum.ActuatorRelativeTo.World ```
You'll notice the MaxForce property there. That's probably the most common "gotcha" for new scripters. If you leave it at the default (which is sometimes 0 or a very low number), your part won't move at all because it doesn't have enough "strength" to overcome gravity or friction. I usually crank it up to something like math.huge if I want a constant, unstoppable movement, but 10,000 to 50,000 is usually plenty for standard parts.
Understanding RelativeTo
This is where people usually get tripped up. The RelativeTo property determines which way "forward" actually is.
- World: If you set it to World,
Vector3.new(10, 0, 0)will always move the part toward the world's X-axis, no matter which way the part is rotated. - Attachment0: If you set it to Attachment0, the movement is based on the orientation of the attachment itself. This is huge for things like rockets or cars. If the part turns, the velocity turns with it.
If you're building a character knockback system, you'll likely use World space to push them away from an explosion. But if you're building a boat script, you definitely want Attachment0 so the boat moves where its nose is pointing.
Making it Dynamic: Knockback Examples
Let's look at a more practical use for a roblox linear velocity script: a knockback effect. Imagine a player gets hit, and you want to fly them backward for a split second.
```lua local function applyKnockback(character, direction) local rootPart = character:FindFirstChild("HumanoidRootPart") if not rootPart then return end
local attachment = Instance.new("Attachment") attachment.Parent = rootPart local lv = Instance.new("LinearVelocity") lv.MaxForce = 100000 lv.VectorVelocity = direction * 50 -- "direction" is a unit vector lv.Attachment0 = attachment lv.Parent = rootPart -- Clean it up after half a second task.wait(0.5) lv:Destroy() attachment:Destroy() end ```
In this case, we're creating the attachment and the LinearVelocity on the fly through the script, then deleting them after a short delay. This prevents the player from flying into space forever. It's a clean, efficient way to handle temporary forces.
Fine-Tuning with ForceLimitMode
Sometimes you don't want the force to be "all or nothing." The ForceLimitMode property is a bit more advanced, but it's worth knowing. You can set it to Magnitude or PerAxis.
Most of the time, Magnitude is what you want—it just puts a cap on the total force. But if you're doing something complex, like a hovering platform that needs a lot of force to stay up (Y-axis) but very little force to slide around (X and Z axes), PerAxis gives you that granular control.
Common Pitfalls and Troubleshooting
If your roblox linear velocity script isn't working, check these three things immediately:
- Is the part Anchored? This is the classic "oops" moment. An anchored part cannot be moved by physics constraints. Uncheck that box!
- Is the MaxForce too low? If your part is heavy (high density), it needs a higher
MaxForceto get it moving. - Network Ownership: If you're trying to move a part from a LocalScript, it might look fine on your screen but won't move for anyone else. For parts not attached to a player, always handle the velocity on the Server. If it's for the player's own character, the client usually has ownership, so a LocalScript can work there.
Why You Should Care About Smoothness
The reason we use LinearVelocity over just changing the CFrame or Position every frame is interpolation. When you manually set the position in a loop, the movement can look jittery or "teleporty," especially if the server lags.
By using a physics constraint, you're telling the Roblox engine: "Hey, I want this object to reach this speed, you handle the math for me." The engine then smooths out the movement between frames, making it look buttery smooth for the players. It also handles collisions way better. If a CFrame-moved part hits a wall, it might clip through it. A LinearVelocity-moved part will actually hit the wall and stop (or bounce), which is exactly what you want in a polished game.
Wrapping Up
Getting comfortable with a roblox linear velocity script is a bit of a milestone for any budding developer. It moves you away from "hacking" things together with position updates and into the realm of proper physics-based game design.
Start small. Try making a part move in a circle by updating the VectorVelocity every frame, or build a simple conveyor belt using the RelativeTo property. The more you mess around with these properties, the more you'll realize just how much power you have over the game world. Physics doesn't have to be scary; it's just a set of rules, and with LinearVelocity, you're the one writing them. Happy scripting!